Filter



oct. 22, 1935. c. w. HANSELL 2,018,358

FILTER Original Filed Sept. 24, 1931 INVENTOR- CLARENCE W. HANSELLATTORN EY- UNITED STATES PATENT OFFICE FILTER Clarence W. Hansell,

Port Jefferson, N. Y., as-

signor to Radio Corporation of America, a corporation of DelawareOriginal application September 24, 1931, Serial No. 564,770. Divided andthis application October 19, 1932, Serial No.

4 Claims.

My present application is a division Vof my copending application,Serial Number 564,770,

iiled September 24, 1931. l

My present invention relates to a filtering sys- 5y tem for use inconnection with alternating current circuits such as radio transmittersor radio receivers. to provide An object of an improved my presentinvention is filtering system utilizing electromagnetic resonators suchas magneto- 1 striction oscillators.

Many lters now in use, or about to be used,

have sloping or imperfect cut-off region characteristics as a result ofall that is 'i for improving the filters especially in which theiraction is not to be desired. To provide apparatus characteristic curvesof such their imperfect cut-olf regions is a further object of mypresent invention. To carry it out, I connect to the ordinary filterhaving this undesirable characteristic a filter such as described in mycopending application or in my present application, which has a sharpcharacteristic in the imperfect region of the ordinary filter and thecombined action of the two produces a filtering system having anexceedingly improved action.

An attempt has invention been made to denne my present withparticularity in the appended may best be understood both organizationand mode of to the accompanying drawof my improved electromagneticfilter;

Figure 2 illustrates a system wherein my improved lilter may be used tosharpen up the characteristic of an ordinary filter; and,

Figure 3 are curves explanatory of my present invention as illustratedin Figure 2.

In carrying out my present invention I make use of magneto-strictionoscillators with overlapping resonance curves, input coils of theoscillators being all connected in parallel with like polarity and theoutput coils are all connected together in series with alternatinglyreversed polarity or vice versa. The coupling between the input andoutput circuits of the filter is established by virtue of themagneto-strictive phenomena and the resonance characteristics of therods whichform the coupling or filter oscillators. The phase of energyfed through this coupling reverses as the frequency passes throughresonance at a frequency intermediate the frequencies of themagneto-strictive rods used. Consequently, polarity of this requires thealternatingly reverse the coils as shown in Figure 1 in order to obtainemcient energy transfer at frequencies corresponding to the overlappingfrequencies of the magnetostrictive elements. In general, it may be saidthat the filters of my present application are more suitable foroperation at lower frequencies than the piezo-electric crystal filtersdescribed in my copending parent application.

In particular, as shown in Figure 1, for low frequencies, I make use ofelectromechanical oscillators in the form of magneto-structionoscillators i2. These magnetc-striction or electromagnetic oscillatorsare made up of any magnetostrictive material such as nickel, whichpossesses the property of converting electromagnetic energy intomechanical energy and vice versa. The input coils lil are connected inparallel and with like polarity whereas the output coils "it arealternatingly connected with reversed polarity. If desired, of course,the coils "it may be considered the input side of the system and coils'i4 the 20 output side of the system, the direction in which energy ispassed by the filter being immaterial. Variable condensers 'i8 areprovided for tuning l the inductance of the oscillators, and, asindicated any form of coupling to other circuits may 25 be used such asdirect, conductive connection or inductive co-upling.

In Figure 1, the tuning of the input and output circuits for the filtersshown not only assist in obtaining the best impedances to use with thefilter but it also suppresses undesired frequencies. Theelectromechanical oscillators, such as piezoelectric crystals andmagnetostriction oscillators and also resonant transmission linesrespond to a series of frequencies and exhibit resonance at 35frequencies approximately in harmonic relation. The tuned input andoutput circuits do not respond to harmonics of their fundamentalfrequencies and so suppress undesired frequencies which would otherwisepass through the filter. 4,0' Thus I combine broadly tuned circuitshaving only one resonant frequency with circuits, or mechanicallyVoscillating equivalents of circuits, which tune sharply for a series offrequencies, to obtain a filter with sharp frequency discrimination butonly one pass band.

As indicated hereinbefore a still further use for my invention is tosharpen up the cut-olf characteristics of the more common types offilters. This may be done by connecting one of my electromechanicallters in parallel with an ordinary filter. Then, if the pass band of theelectromechanical filter lies in the imperfect cut-off region of theordinary 'filter it will extend the pass band of the ordinary filter andthe cut-off charactero c of the ordinary filter,

istics of the combination will be that of the electromechanical filter,which is very sharp, while the width of pass band will be substantiallythat of the ordinary filter.

Referring to Figure 2 wherein such an arrangement is shown, an ordinaryfilter is paralleled with an improved filter 82 according to my presentinvention.

The input coils 14, shown in Fig. 2, are all so connected and wound thatcurrents flowing from the common lead to all the coils will fiow throughthe coil windings in like directions around the rods and at any giveninstant tend to magnetize the rods with like polarity.

The output coils 16, on the other hand, which are shown connected inseries, are Wound in alternately opposite directions. A common currenttraversing all the coils will flow around a rod having a given frequencyresponse band in a given direction but will fiow in an oppositedirection around a rod responsive to a next adjacent overlappingfrequency band.

Likewise, the ouput coils may all be wound in the same direction andthen connected together in series with their terminals alternatelyreversed. This will give the same result as if the coils were woundoppositely.

The characteristic curve of the ordinary filter is given by curve c ofFigure 3, and the characteristic curve of filter 82 is given by curve dof Figure 3, and the improved characteristic of the combined filters isgiven by curve e of Figure 3.

VIf it is desired to sharpen up both ends of curve it should beparalleled by another of my improved iilters having a band passcharacteristic corresponding in frequency to the other end of thefrequency range of the ordinary iilter whose curve is illustrated bycurve c of. Figure 3.

It will be noted that I have shown a somewhat triangular shapedcharacteristic for the electromechanical filter to make it correct theordinary filter more perfectly. I may obtain this triangularcharacteristic by Varying the number of turns in the coils of themagneto-striction oscillators as shown or I may use various sizes ofseries impedances with any form of electromechanical vibrator.

In the crystal filter, such as Figure 5 of my copending application, Imay obtain the desired results by varying the sizes of the crystalelectrodes or by varying the couplings to either input or outputelectrodes or both. In fact any method for varying the effectiveness ofthe individual vibrators, including the application of damping, may beused whereby the combination 5 of filters give the desiredcharacteristic.

Having thus described my invention, what I claim is:

1. A filter circuit comprising a plurality or magneto-strictionoscillators having overlapping 10 resonance curves, each of saidoscillators having an input circuit and an output circuit, means forconnecting a group of, like circuits of said oscillators in parallelwith like polarity, and, means for coupling the other circuits of saidoscillators 15 effectively in series, some of the other circuits beingconnected with relatively reversed polarity with respect to said groupof circuits in parallel.

2.. Apparatus for selectively passing energy of a band of frequenciescomprising a plurality of 20 electromagnetic vibrators, said vibratorshaving symmetrical, displaced overlapping resonant circuits and each ofsaid vibrators having a pair of coils, means for connectingcorresponding coils located on one end of said vibrators in series, 8iand means for connecting the other corresponding coils of said vibratorslocated'on an end opposite from said series connected coils in parallel.

3. A band pass filter comprising a plurality of wl electromagneticvibrators each ot said vibrators having a different resonant frequency,a pair of coils operatively associated with each of said vibrators,means for connecting the coils located on one end of said vibrators inparallel, and 85 means for connecting other like coils of each pair ofcoils located on an end opposite from said parallel connected coils inseries.

4. A band pass filter comprising a plurality of electromagneticvibrators each having a different 40 resonant frequency, said vibratorshaving an input circuit and an output circuit, a pair of coils locatedat each end of said Vibrators, means for connecting each of the coilslocated on one side of said vibrators in parallel, and means for 45connecting each of. the coils located at the other side of saidvibrators in series, and tuning condensers operatively connected in boththe input and output circuits to tune the coils of said vibrators.

' CLARENCE W. HANSELL.

